According to the prior art, means is provided for conveying articles circulatively in a horizontal position on both going and returning sides. Such a means is disclosed, for example, in the specification and FIG. 2 of Japanese Laid-open Patent Application No. 32415/1992. As shown in this reference, two endless chains moving circulatively in a vertical plane are disposed side by side while being out of phase with each other in a longitudinal direction. Loading bases are fixed to ends of support rods which are mounted to the endless chains rotatably with such phase difference.
In the above-mentioned art, it is difficult to maintain the synchronous operation of both endless chains at the same speed because both chains are different in point of elongation. Furthermore, rolling occurs due to loosening of the chains and hence it is not easy to allow the loading bases circulate in a horizontal position.